The Gun Counter

A friend of mine has a 5.56 caliber AR pistol with a 10.5" barrel. It goes bang, but with some frequency fails to eject the spent brass, then attempts to feed that piece of brass and a new round at the same time. The result is damage to the new round and a double feed jam. As you can imagine, this creates a hell of a mess.

He is also having the same issue with a 308 caliber full sized Ar-10.

I have very little experience with the AR-10 platform, but I am thinking the Ar-15 is too lite of a buffer and the recoil is hammering the bolt back too fast and it is rebounding back before and ejection can occur. Thus a stiffer spring or heavier buffer would be the cure.

Is this good thinking or is something else the likely cause?

I haven't messed with that much, but I was thinking buffer spring, too. I wonder if it's too heavy, so the bolt doesn't get far enough back to eject the spent case?

Or, maybe the buffer is too heavy, so it's moving to slowly to get all the way back?

I'd speculate that there's less pressure in a shorter barrel to move the BCG back as far or as hard?

My 300blk SBR did something similar and the solution was to put an o-ring under the extractor.

It could be two things based on the number of pistols I built over time. One, it's going to fast and not grabbing the brass, that requires a heavier buffer and usually solves the problem. The other one is it is not getting enough gas and short stroking, that may be an adjustment of your gas tube. Did he build it himself? Was it a kit or just "parts"?

Thanks guys.
I have heard something about the O-ring under the extractor before. What does that do? I mean I know it fixed the issue, but how.
The lower is a stripped lower that he built. The upper is a complete upper from not sure who. He told me but I forget.

The AR-10 was purchased as a complete gun.

Gave him the above info. Will see what happens.

The o-ring increases the tension on the extractor so that it actually extracts. There's also a black stem that is some kind of plastic or poly that is supposed to be in there with the spring and the o-ring as well IIRC. Also IIRC, my rifle only had the problem with supersonic ammo; subs functioned fine so it was a case of the extractor slipping off the rim with the more violent extraction. 10" 300blk with an H2 buffer. There's probably old posts somewhere on this forum about it.

Here we go, the o-ring info is several pages in.

https://www.theguncounter.com/forum/vie ... =5&t=26283

I have seen this failure on mine when testing light loads (while trying various loads from light up to heavy during load development).

What is the position of the empty case(s) in the double feeds? Are they going nose in to the feed ramps? Angled? Stovepipe? Are they even making it clear of the chamber?

One thing that I haven't seen brought up is it could also be an ejector problem - the brass isn't getting kicked hard enough to pop out the way it should.

With the pistol, though, I would think that the buffer/spring combo is most likely the culprit, followed by the extractor. The shorter the gas tube, the higher the gas pressure (due to being closer to the chamber, thus the gas has had less space to expand into before it reaches the gas port), and thus the faster the bolt group is going to be moving. The balance for that is a heavier buffer and/or a stronger spring. All of my carbines have H1 or H2 buffers. I've never had an AR pistol, but I'd imagine they need at least an H2.

If the AR-10 is a factory rifle, it shouldn't have an issue with the buffer or spring. (Shouldn't, although it's possible, I guess) That makes the extractor the most likely problem.

I'm going to say short stroking is unlikely, because the bolt is going back far enough to pick up the fresh round.

Could it be overgassed?

I think I suggested that already